Integrated circuits can be adversely affected by rapid and unpredictable environmental changes, such as bursts of radiation or high temperatures. Of particular concern in military applications is the data corruption that can occur due to extraneous memory write errors resulting from a transient dose.
The term transient dose is used to describe the effect on an integrated circuit of a burst of radiation, such as x-ray and gamma ray radiation from a nuclear explosion. A photocurrent pulse can be induced when such radiation generates electron-hole pairs that are separated by ambient electric fields.
At high enough levels, a radiation dose can cause data corruption due to photocurrent in the memory cells and/or a lowering of supply voltage to the cells due to total chip photocurrent. In addition, false memory WRITEs can be caused by transient dose induced noise at the input to the memory chip that is coupled into memory write circuits, causing extraneous WRITE operations that corrupt data stored in the memory.
Current efforts to protect sensitive integrated circuit components from transient dose effects focus on off-chip transient dose detectors designed to detect a radiation burst. The detector provides an event signal to a controller, which responds by disabling memory WRITE operations. Typically, the detector includes means to cause the system to reboot after event detection and WRITE disable.
A problem with current off-chip approaches to transient dose detection is response time--the time for event detection, event signaling and WRITE disable is such that a significant number of extraneous data-corrupting WRITEs can still occur. An additional problem is controller reliability in a transient dose environment.
Accordingly, a need exists for an integrated circuit mechanism to improve the response time for detecting transient events, such as for the purpose of disabling memory WRITE operations before any significant number of data-corrupting WRITE operations occur. Preferably, such a transient event detector could be configured to provide asymmetrical control, allowing rapid event detection and response followed by time-delayed system reset.